The present invention generally relates to a high frequency circuit arrangement, and more particularly, to an electrical trap construction comprising a coaxial cable or coaxial resonator for use in a high frequency circuit device of compact size.
Conventionally, for a band-pass filter employing a plurality of dielectric coaxial resonators, there has been proposed an arrangement, for example, as shown in FIG. 1, which generally includes a casing H having an input side connector Ic and an output side connector Oc, a plurality of dielectric coaxial resonators R each including a cylindrical ceramic dielectric member, inner and outer conductive electrode layers respectively formed on corresponding inner and outer peripheral surfaces of the cylindrical ceramic dielectric member and another electrode layer formed on one end face of said dielectric member so as to shortcircuit the inner and outer conductive electrode layer to each other for resonance at a 1/4 wavelength, and coupling capacitors C for coupling the respective coaxial resonators R.
The coupling capacitors C are inserted in series in a hot signal line L between the input connector Ic and the output connector Oc, while terminals (not shown) fixed to the inner conductive electrodes of the respective resonators R are connected between said coupling capacitors C, with the outer conductive electrodes thereof being grounded, thus constituting a band-pass filter F. The arrangement of FIG. 1 further includes an electrical trap T for suppression of spurious signals. The trap T is constituted by a dielectric coaxial resonator Rt having the construction similar to that of the resonators R, a capacitor Ct connected, at its one end, to an inner conductive electrode layer of the resonator Rt and, at its other end, between the neighboring coupling capacitor C and the output connector Oc, with an outer conductive electrode layer of said resonator Rt being grounded, thereby to produce a series resonance at the spurious frequency to be suppressed, by an inductance presented by the resonator Rt and the capacitor Ct.
The trap construction as described above with reference to FIG. 1, however, has the drawback that the separate space required for accommodation of the coaxial resonator Rt and capacitor Ct within the casing H limits the degree to which the size of a device incorporating the trap can be reduced.